1. Field of the Invention
The present invention relates to a coordinate detecting device.
2. Description of the Related Art
Touch panels have been used, for example, as input devices for computer systems. A touch panel mounted on a display can detect coordinate positions on the display and obtain detection signals corresponding to the coordinate positions. Touch panels allow direct, easy, and intuitive input of data.
There have been suggested various types of touch panels such as resistive type, optical type, and capacity coupling type touch panels. The resistive touch panels having a simple structure and control system are predominantly used. As resistive touch panels, there are a four-wire type, a five-wire type, an eight-wire type touch panels, and the like depending on an arrangement of electrodes over a resistive film.
Among these, in the five-wire type touch panel, a conductive film of a top substrate provided on an operations surface side is simply used only for reading potentials, which is different from the four-wire type and eight-wire type resistive touch panels. Thus, the five-wire type touch panel does not have a problem of edge sliding, which is a defect of the four-wire type and eight-wire type touch panels. Therefore, the five-wire type touch panels have been used in markets that demand durability in a severe usage environment or over a long time.
FIG. 12 is a configuration diagram of a five-wire type resistive touch panel. A five-wire type resistive touch panel 1 is formed of a top substrate 11 and a bottom substrate 12. As the bottom substrate 12, a transparent resistive film 22 is formed all over a surface of a glass substrate 21. Over the transparent resistive film 22, X-axis coordinate detecting electrodes 23 and 24, and Y-axis coordinate detecting electrodes 25 and 26 are formed. As the top substrate 11, a transparent resistive film 32 is formed over a film substrate 31. A coordinate detecting electrode 33 is formed over the transparent resistive film 32.
First, by applying a voltage to the X-axis coordinate detecting electrodes 23 and 24, a potential distribution is generated in a direction of the X-axis of the transparent resistive film 22 of the bottom substrate 12. At this time, by detecting a potential of the transparent resistive film 22 of the bottom substrate 12, an X-coordinate of a contact position of the bottom substrate 12 with the top substrate 11 can be detected. Next, by applying a voltage to the Y-axis coordinate detecting electrodes 25 and 26, a potential distribution is generated in a direction of the Y-axis in the transparent resistive film 22 of the bottom substrate 12. At this time, by detecting a potential of the transparent resistive film 22 of the bottom substrate 12, a Y-coordinate of a contact position of the bottom substrate 12 with the top substrate 11 can be detected.
In this case, in such a type of touch panel, there is a problem in how to generate an even potential distribution in the transparent resistive film 22 of the bottom substrate 12. To generate the even potential distribution in the transparent resistive film 22 of the bottom substrate 12, a method to provide plural stages of potential distribution correction patterns in a periphery is disclosed in Patent Document 1.
Further, Patent Document 2 discloses a method to provide a common electrode so as to surround a periphery of an input surface. Patent Document 3 discloses a method to form an opening in an insulating film provided over a transparent resistive film and to apply a potential through the opening.
Patent Document 1: Japanese Patent Application Publication No. 10-83251
Patent Document 2: Japanese Patent Application Publication No. 2001-125724
Patent Document 3: Japanese Patent Application Publication No. 2007-25904
Coordinate input devices are required to be narrower in frame size in response to the downsizing and the like of devices to which the coordinate input devices are mounted. However, it has been difficult to form the coordinate input device disclosed in Patent Document 1 with a narrower frame since it is necessary to provide plural stages of potential distribution patterns in a periphery.
Moreover, by the method to provide a common electrode to surround a periphery of an input surface as disclosed in Patent Document 2, there has been a problem in that the potential distribution of a transparent resistive film becomes uneven unless a resistance ratio between the transparent resistive film and a pattern resistance is increased.
Furthermore, although the aforementioned two problems can be solved by the method to provide an opening in a formed insulating film as disclosed in Patent Document 3, a manufacturing process becomes complicated in this case. In particular, there have been some cases that variations of materials and resistance values caused in the manufacturing process become a factor to decrease a yield of a desired product property.